Using a sharp veggie peeler, shave the celery to get long thin shavings. Put the celery shavings in ice water with half a lemon and its juice and let sit for at least 1 hour or overnight in the refrigerator. The celery will get very crunchy, curly and cute.
Bring a pot of well salted water to a boil, over medium heat and set up a bowl of well salted ice water. Toss the haricots verts in the boiling water and cook until the beans are tender but still firm. Remove the beans from the boiling water and plunge immediately into the ice water and let them cool. When they are cold and still vibrantly green, remove them from the ice water and reserve.
Season the fish fillets with salt. Combine the herbs and the potato flakes in a shallow dish. Dip the flesh side of each fillet into the egg wash and then press them into the herb/potato flake mixture. Put on a sheet tray with the crusted side up.
To cook and assemble everything:
Preheat the oven to 350 degrees F.
Coat a large saute pan with olive oil and heat it over medium-high heat. When the oil is hot but not smoking, add the fish, crusted side down. When the crust has become golden and crispy, flip them over, then transfer the fish to a baking sheet lined with a cooling rack and put in the preheated oven for 5 to 6 minutes.
Remove the oil in the saute pan and add new oil. Toss in the garlic and crushed red pepper. When the garlic becomes golden and aromatic remove it and discard. Toss in the reserved haricots verts, season with salt, to taste, and roll them around in the oil to heat through. When they are hot, turn off the heat and reserve them in the pan.
Remove the celery from the ice water and dry in a salad spinner to remove the excess water. Add the celery to the pan with the beans. Squeeze in the juice from the remaining lemon half and season with salt, if needed.
Divide the veggies between 4 serving plates and top with the crusted fish.